This invention is directed to the chemical treatment of wood and other cellulosic materials to render them fire retardant. More particularly, this invention is directed to synergistic fire retardant compositions which are substantially non-hygroscopic consisting essentially of the partial reaction product of dicyandiamide, phosphoric acid, boric acid and water.
It has become the practice in the wood treating industry to treat wood with chemical compounds to preserve the wood. Chemicals suggested for this purpose include ammonium phosphate, ammonium chloride, ammonium sulfate, phosphoric acid, zinc chloride, and magnesium chloride. These chemicals are impregnated as solutions into the wood where they are deposited within the pores of the wood when the solution evaporates. However, these chemicals are only suitable for treating wood which is not subject to the leaching effect of rain and/or ground water. These chemicals are not suitable for exterior and underground construction where leach resistant fire retardants are necessary. In addition, some of these chemicals are objectionable because they are very corrosive to any metal which may be in contact with the treated wood. Some of the chemicals also cause an objectionable afterglow with the wood and are detrimental to the structural strength of the treated wood. Moreover, many of these chemicals are hygroscopic which causes the wood to absorb moisture and bloom which makes their use objectionable. More recently, there has been a trend in the wood treating industry towards fire retardant chemical treatments which have low hygroscopicity and are leach resistant and which can be used for exterior wood. Many of these fire retardant chemical treatments for exterior wood have been based on amine-aldehyde-phosphorus condensation compounds. In accordance with the general practice, wood is impregnated with a solution of an incompletely reacted amine-aldehyde-composition together with an oxy acid of phosphorus. The impregnated wood is then dried and cured.
For example, Goldstein et al., U.S. Pat. No. 2,917,408 disclose the preparation of fire retardant wood with a combination of dicyandiamide and phosphoric acid, and Goldstein et al., U.S. Pat. No. 3,159,503 disclose the preparation of fire retardant wood with a combination of dicyandiamide, phosphoric acid and very small amounts of formaldehyde. In addition, Juneja, U.S. Pat. No. 3,832,316 discloses a composition for imparting fire retardancy to wood comprising dicyandiamide, melamine, formaldehyde, and phosphoric acid and suggests that minor amounts of other materials may be substituted for some of the phosphoric acid, such as boric acid, and Juneja, Canadian Pat. No. 917,334 discloses a composition for treating wood to impart fire retardancy thereto comprising dicyandiamide, urea, formaldehyde and phosphoric acid and suggests that minor amounts of other materials may be substituted for some of the phosphoric acid, such as boric acid. Other similar patents include U.S. Pat. Nos. 2,935,471; 3,137,607; 3,874,990 and 4,010,296.
While most of the above described chemical compositions based on dicyandiamide, melamine, urea, formaldehyde and phosphoric acid are effective for imparting fire retardancy to wood, they suffer from one or more drawbacks. Compositions containing solids of more than about 15 percent urea render the wood hygroscopic. Further, these compositions containing formaldehyde tend to be resinous and require high drying temperatures of about 100.degree. C. to 110.degree. C. to completely cure the resin, thereby impairing the strength of the wood.